1. Field of the Invention
A "dip-stick" immunoassay provides a simple and rapid technique for measuring the presence and amount of an analyte in a sample solution. The analyte may be present in serum, urine, saliva, etc. and may consist of any of a wide variety of materials, such as drugs, naturally occuring physiological compounds, pollutants, or the like.
Various signal producing techniques are employed for developing a detectable signal related to the presence or amount of an analyte. One desirable system employs horse radish peroxidase to oxidize a dye precursor to a dye. Ascorbate affects this reaction so that the amount of dye which is produced can vary with the amount of ascorbate present in the assay medium.
Since samples, which are assayed are frequently physiological fluids having widely varying amounts of ascorbate, unless the ascorbate interference can be diminished to a satisfactory level, the assay can only provide erratic and uncertain results. It is therefore desirable to find a simple efficient and economic way for reducing ascorbate interference without otherwise interfering with other assay reagents or increasing the complexity of the protocol.
2. Brief Description of the Prior Art
The basic dipstick immunoassay technique is discussed at length in U.S. Pat. No. 4,299,916. A pretreatment of serum prior to an assay of thyroxine is disclosed in U.S. Pat. No. 4,121,975. The addition of soluble iodate to eliminate interference from reducing agents when detecting redox reactions is disclosed in European Pat. No. 76,076D. The use of HIO.sub.4 and/or its salts to remove interfering reducing substances is disclosed in Japanese Patent Application No. 81/109,595.